1. Field of the Invention
The present invention relates to an electrode producing method. More particularly, the present invention relates to an electrode producing method in which metal bars for an electrode can be welded together efficiently.
2. Description Related to the Prior Art
A camera has an electronic flash device, which includes a flash discharge tube. The flash discharge tube has a glass vessel and xenon gas enclosed therein. Pin-shaped electrodes are positioned through end portions of the glass vessel. For flash emitting operation, a main capacitor is discharged, so that charge passes between the pin-shaped electrodes to emit flash light instantaneously.
Each of the pin-shaped electrodes includes an electrode core and a lead connected therewith. The electrode core is contained in the glass vessel, and formed from tungsten (W). The lead protrudes externally from the glass vessel, and is formed from nickel (Ni) or manganese-nickel (Mnxe2x80x94Ni). To obtain the pin-shaped electrode, an end of a tungsten bar is welded on to an end of a nickel lead. Specifically, an electric current is caused to flow between the tungsten bar and the nickel lead while the end of the tungsten bar is kept butting on that of the nickel lead. The end of the nickel lead is melted, and wraps the end of the tungsten bar for the welding, because the nickel lead has a considerably low melting point. A ball-shaped melted portion is formed at the end of the nickel lead being welded, and is used for positioning the pin-shaped electrode in the glass vessel.
A ring-shaped cathode part is attached to the tungsten bar of the pin-shaped electrode being a cathode, and formed from sintered metal including cesium compound, and operates for raising efficiency in emission of electron. The ring-shaped cathode part has a central hole, in which the pin-shaped electrode is inserted. The ring-shaped cathode part is depressed and deformed, and attached to the pin-shaped electrode by caulking. For the purpose of tightening the caulking, a surface of the tungsten bar of the pin-shaped electrode is provided with a random pattern of minute recesses or scratches.
The ball-shaped melted portion formed between the tungsten bar and the nickel lead is required to have a regularized shape and size for the purpose of positioning the pin-shaped electrode in the glass vessel. However, the shape of the ball-shaped melted portion changes according to various conditions of welding, and is difficult to have a regularized common shape.
In the conventional technique for the pin-shaped electrode, the random pattern of recesses or scratches is formed by cutting, scraping or abrading or in other manners at the time of manufacturing the tungsten bar. However, the number of steps of creating the random pattern is considerably great. So the cost for producing the pin-shaped electrode cannot be reduced because of the complicated processes.
In view of the foregoing problems, an object of the present invention is to provide an electrode producing method in which metal bars for an electrode can be welded together efficiently, to produce the electrode at a low cost.
In order to achieve the above and other objects and advantages of this invention, an electrode producing method of producing a pin-shaped electrode for a flash discharge tube is provided, the pin-shaped electrode including a first bar of metal having a first end portion, and a second bar of metal having a second end portion connected with the first end portion. In the electrode producing method, the first and second bars are retained by use of respectively first and second chuck mechanisms with the first and second end portions opposed to one another. The first and second end portions are pushed on one another by moving at least one of the first and second chuck mechanisms. While the first and second end portions are pushed on one another, the first and second chuck mechanisms are supplied with electric current, so as to weld the first and second bars together therewith by resistance welding.
In the welding step, the second end portion is melted to form a ball-shaped melted portion, the ball-shaped melted portion is secured by wrapping the first end portion.
The flash discharge tube includes a vessel having discharge gas enclosed therein. A second pin-shaped electrode is inserted through and secured to the vessel. The pin-shaped electrode is inserted through the vessel, the second bar extends externally from the vessel, the first bar is disposed in the vessel, and opposed to the second pin-shaped electrode. The ball-shaped melted portion is positioned on an outer surface of the vessel.
Furthermore, a protruding amount of the first bar from the first chuck mechanism is adjusted before the second chuck mechanism supplies the second bar.
The ball-shaped melted portion after welding has a greater diameter than a thickness thereof as viewed in an axial direction of the pin-shaped electrode.
The first and second chuck mechanisms include first and second two-way chucks, the first two-way chuck squeezes the first bar in a first squeezing direction, the second two-way chuck squeezes the second bar in a second squeezing direction, the first and second squeezing directions are substantially perpendicular to one another.
The first bar has a diameter Dw, and the protruding amount of the first bar from the first chuck mechanism is from 0.6xc2x7Dw to 1.5xc2x7Dw.
The first bar includes tungsten.
The pin-shaped electrode is a pin-shaped cathode, and further includes a ring-shaped cathode part secured to the first bar. Furthermore, a surface of the first bar is subjected to surface processing. The cathode part is secured to the first bar after the surface processing.
According to another aspect of the invention, an electrode producing method of producing a pin-shaped electrode for a flash discharge tube is provided, the pin-shaped electrode including a first bar of metal and a ring-shaped cathode part, secured to the first bar, for raising efficiency in emitting electron. In the electrode producing method, a recess is formed in the first bar by applying laser light thereto. The cathode part is secured to the recess.
Furthermore, gas is blown over the first bar during the recess forming step, to blow away metal dust created by forming the recess.
The first bar has a first end portion disposed on a farther side from the cathode part. The pin-shaped electrode further includes a second bar of metal having a second end portion connected with the first end portion. Furthermore, the second bar is connected with the first bar before the recess forming step.
The cathode part has a size Lc in an axial direction of the pin-shaped electrode, and the recess has a width from 0.1xc2x7Lc to 1.5xc2x7Lc in the axial direction.
The first bar has a diameter Dw, and the recess has a depth from 0.03xc2x7Dw to 0.4xc2x7Dw.
The cathode part includes cesium.
According to still another aspect of the invention, the first bar is provided with surface roughness by subjecting the first bar to sandblast processing. The cathode part is secured to the first bar after the sandblast processing.
Furthermore, the cathode part is pressurized and deformed, to attach the cathode part to the first bar.
The first bar has a first end portion disposed on a farther side from the cathode part. The pin-shaped electrode further includes a second bar of metal having a second end portion connected with the first end portion. Furthermore, a step of connecting the second bar with the first bar before the sandblast processing.
Consequently, the metal bars for an electrode can be welded together efficiently, to produce the electrode at a low cost.